Ramon Espinosa, Associated Press - ApFILE - Australian swimmer Chloe McCardel waves to spectators as she begins her swim to Florida from the waters off Havana, Cuba, in a Wednesday, June 12, 2013 file photo.

KEY WEST, Fla. — The Australian who gave up her quest to swim from Cuba to Florida because of painful jellyfish stings said Thursday that she will not make another attempt.

Chloe McCardel told The Associated Press that she had picked June because the jellyfish danger was supposed to be low. But about 11 hours and 14 miles into her expected 60-hour, 110-mile journey, she found herself in a swarm.

"I had one coming out of my mouth. I was pulling it, this tentacle out of my mouth, but I don't remember this moment. My kayaker told me that I was doing this, 'cause I have no recollection. I'm not coming back. That's it," she said.

The 28-year-old from Melbourne became the latest endurance athlete undone by the strong currents and fierce jellyfish of the Florida Straits on Wednesday night, abandoning her attempt to become the first person to swim across nonstop without a shark cage. The jellyfish caught her by surprise.

"I got smashed with them coming from every direction," she said. "I would not have gone to all this trouble if I had known they would be out in such numbers in June."

She was pulled out of the water and taken by one of her support vessels to Key West, where she was resting at a hotel Thursday. She said the trip back to land was excruciating.

Ramon Espinosa, Associated Press - Ap

Australian swimmer Chloe McCardel waves to media before jumping into the water at Hemingway Marina to start her swim to Florida from Havana, Cuba, Wednesday, June 12, 2013.

"It was two and a half hours of the worst pain, continuously, every second, of my whole entire life. It's like fireballs in every fiber," she said.

It was the fifth failure involving three women who have tried to make the marathon swim the past three summers. Jellyfish stings and strong currents have been the main impediments.

Diana Nyad tweeted her commiseration. The endurance athlete has failed three times trying to make the same crossing and says she'd like to take another shot this summer.

"It's a tough night for Chloe McCardel, a superior swimmer and an exemplary spirit," Nyad wrote.

Endurance swimmer Penny Palfrey has also tried and failed to make the swim.

Australian Susie Maroney successfully made the crossing in 1997, but she did it with the benefit of a shark cage.

McCardel had twice made a double crossing of the English Channel, but the most time she had spent in the water continuously was 25 hours.

She attempted her Cuba to Florida swim under English Channel Marathon rules, which meant she could not touch her support boat or hold on to anything. She also wasn't allowed to wear a full-body wetsuit, which would have helped protect against jellyfish.

McCardel and her team spent nine and a half months planning the trip and studying others' attempts.

The repeated failures raise the question of whether the Cuba-to-Florida swim without a cage is even doable as a 2.5 day swim is stretching the physical limits of even elite endurance athletes. According to the Guinness Book of World Records, the longest open water swim without flippers was 139.8 miles (225 km) by Croatian Veljko Rogosic, who swam between two Italian cities on the Adriatic Sea from Aug. 29 to 31, 2006.

Dr. Clifton Page, a sports medicine specialist at the University of Miami Miller School of Medicine, said he thinks the Cuba-to-Florida swim can be done, although there are several physical obstacles to overcome. He has advised Nyad on her swims.

One obstacle is hypothermia. While the water is more than 80 degrees in late spring and summer, it is still well below the body's normal temperature of 98 degrees and causes it to slowly drop. There is also malnutrition. No matter how often the swimmer stops to eat, she will never ingest enough calories to make up for those expended swimming, he said. After a while, that causes the muscles to start breaking down. Then there is dehydration, he said. Even though swimmers don't feel it, they sweat just like any other athlete, while the saltwater acts like a wick, drawing even more water out of the body. Finally, there is sleep deprivation -- exercising that hard for days without sleep can result in hallucinations.

"The variable is the jellyfish," Page said. He said their bites are very painful and potentially fatal if not treated. "Chloe would have gotten a lot further into her swim if she hadn't been bit."

Adding to the swimmer's strain are the Florida Strait's currents. Villy Kourafalou, a University of Miami oceanography professor, said that the swim from Cuba to the Keys "is very challenging as the currents are not only very strong but also extremely variable."

But, she said, modern computer models that utilize information from satellites, buoys and ships allow the swimmer's support team to better predict the currents and help the members decide the best time to start the swim, the best route to take and then make adjustments along the way.